Question

The contractile vacuole is responsible for maintaining the water balance in many protists, like the Euglena above. Maintaining this water balance is an example of A. equilibruim B. homeostasis C. active transport D. passive transport

Answer 1

>:( I had a long explanation for this & the wifi spazzed out & now it's gone.

It's B, because homeostasis is the maintaining of stable internal conditions within an organism. If a contractile vacuole expels water, it's so the cell/protist can still function without being overrun with water & thus "drown," not being able to function.
I was going to have such a more thorough explanation than this. Ugh.
Hope this helps, though!